Software developer Denis Hennessy approached this question kinda like the price-per-pound approach he uses when buying groceries. With batteries, he looked at cost per watt-hour.

Hennessy bought a bunch of AA cells, and tested them on a homemade circuit built from an Arduino controller and an LCD monitor. The apparatus sucked a full charge out of each battery, one at a time, using a fixed resistive load. As the battery drained, the LCD gave a second-by-second display of voltage and the amount of energy generated, in Joules and watt-hours. Once the charge dropped below 0.2V, the circuit stopped logging and showed the total amount of energy the battery had produced. As each battery bled out, he compared its cost and performance to compute a price per watt-hour.

Hennessy tried out various recognizable brands—Duracell, Panasonic, and Energizer—each with super-charged names such as "ultra," "plus power," and "industrial." He found that those alluring adjectives don't really mean much. The best value AAs came from RS Power Ultra, which was more than nine times better than the worst, the Panasonic Evolta.

Now, this test took place in the EU, so you can't actually get the RS Power Ultra here in the states. You can, however, recreate Hennessy's test, because he's posted the source code, design, and result files on GitHub. [Dennis Hennessy via HackaDay]